Gaskets have numerous uses that typically involve providing a seal between two opposing surfaces. A gasket may be used, for example, to provide a seal between the internal surfaces of a head member or an intake manifold or an oil filter and the external surface of an engine block, or the internal surfaces of a mold (e.g., a mold used to prepare plastic articles). In many applications, a gasket is compressed between opposing surfaces under static conditions, which are maintained until the opposing surfaces are separated and the seal there-between is broken (e.g., as is the case with an engine oil filter or a plastic injection mold apparatus).
In certain applications, a gasket must maintain a substantially constant seal between opposing surfaces under dynamic conditions, in which the distance between the opposing surfaces is increased and/or decreased (e.g., the opposing surfaces being moved between first and second positions). Examples of applications that require a substantially constant seal under dynamic conditions include, multi-injection molding of plastic articles, and in-mold coating of molded plastic articles. In addition, the distance between opposing surfaces may vary as the result of a combination of the surfaces being fabricated from materials having different coefficients of linear expansion and temperature fluctuations, thus necessitating the need for a gasket that is capable of maintaining a substantially constant seal under such dynamic conditions.
With in-mold coating methods, a plastic material (e.g., a thermoplastic material) is typically first injected into a mold apparatus to form a molded plastic article. The distance between the opposing dies of the mold apparatus is increased, and a coating composition is then injected into the mold, thereby forming a coated molded article. See for example, U.S. Pat. No. 4,076,788. During the plastic injection and coating injection steps, the gasket employed must maintain a substantially constant seal between the opposing dies of the mold apparatus. If the seal is not sufficiently maintained, the injected plastic material and in particular the injected coating material may undesirably leak out of the mold apparatus resulting in wasted material, fouling of the mold and/or the formation of a coated molded article having defective coating surfaces.
It would be desirable to develop a gasket that provides a substantially constant seal between opposing surfaces under dynamic conditions (e.g., as the distance between the opposing surfaces is increased and/or decreased). It would further be desirable to develop an improved method of forming a coated molded article that makes use of such a dynamic gasket.